The Rcmdr menu item
Statistics > Means > One-way ANOVA...
has a checkbox for pairwise comparison of means"
It uses glht in the multcomp package.

The second option, which I prefer, is to use the MMC (Mean-mean Multiple
Comparisons) plot. I describe the one-way ANOVA use here. See the help
file for higher-order designs and user-specified contrasts.

If the means of the groups are close together, you might need to check
the box for the tiebreaker plot. You will need to record graph history if
you
need the teibreaker plot as it appears on a second page.